BLACK RIVERAN STAGE

division of Ordovician time in North America (the Ordovician Period began about 500,000,000 years ago and lasted about 70,000,000 years); the Black Riveran precedes the Trentonian Stage and follows the Chazyan Stage of the Champlainian Series. The type area for the Black Riveran is to be found in the exposures in the cliffs along the Black River of New York. Black Riveran rocks consist largely of marine limestones, although shales bearing fossil graptolites are also known. Several layers of volcanic ash are found interbedded with Black Riveran limestones.